Radio direction finder



1947. o. G. c. LUCK 2,432,777

, RADIO DIRECTION FINDER Filed Sept. 30, 1942 Patented Dec. 16, 1947 UNITED STATES PATENT OFFICE David G. C. Luck, Hightstown, N. .L, assignor to Radio Corporation of America, a corporation of Delaware Application September 30, 1942, Serial No. 460,293

, F 6 Claims. (01. 250-11) This invention relates to radio direction finders and more particularly to the elimination of errors caused by anomalous response of an Adcock antenna system. The most serious instrumental errors of direction finders are caused by currents introduced in the circuits fed by the antennas as a result of pickup on conductors other than those intended to act as antennas. Such errors are usually but somewhat inaccurately called polarization errors, because the undesired type of pickup often occurs most strongly in radiation fields polarized so that the conductors intended to act as antennas are not excited efl ciently.

In a directon finder of the Adcock type comprising spaced vertical rod antennas connected in push-pull pairs to their respective load circuits, error producing pickup may occur primarily on the horizontal leads' connecting the individual antennas to the associated apparatus. Serious errors of this type remain even in the shielded-U Adcock systems, where the leads are incorporated in or buried under a conductive ground mat. The manner in which stray pickup errors come about in a shielded-U Adcock system is not completely understood at the present time. One possibility is that signal currents flowing in the finite impedance of the ground mat set up voltages between regions thereof adjacent the individual antennas, and these voltages are coupled into the antenna circuits through the capacitances of the respective antennas to the ground mat. A remedy forst-ray pickup of this type is described in U. S. application, Serial Number 456,495, filed August 28, 1942, by D. G. C. Luck.

Another possible sourceof the trouble is the necessary dissymmetry of the surroundings of each antenna. The presence of the other antenna of the Adcock pair itself destroys the symmetry of the surroundings for each antenna, and each antenna is also unsymmetrically placed with respect to the ground mat.

Accordingly it is an object of the invention to provide an improved method of and means for eliminating anomalous responses of an Adcock antenna system.

A further object is to provide an Adcock array with a plurality of loaded dummy or inactive antennas, so placed with respect to the active antennas that the surroundings of each of said active antennas are substantially symmetrical.

These and other and incidental objects will become apparent to those skilled in the art upon consideration of the following description, with reference to the accompanying drawing, of which Fig. 1 is a plan view of a four-antenna fixed Adcock system, Fig. 2 shows an array including dummy antennas at the ends of each line of active antennas, Fig. 2a is a schematic circuit diagram of the connections of the antennas of Fig. 2, and Figs. 3-6 are similar plan views of several modifications of the invention.

Referring to Fig. 1, the usual fixed antenna shielded-U Adcock system comprises four vertical rods N, E, S and W, arranged at the corners of a square and equidistant from the center of a conductive ground mat, G. The antennas are connected in pairs NS and EW by shielded horizontal conductors to their respective load or utilization circuits in a direction indicator T. Consideration of Fig. 1 shows that although the two pairs, NS and EW, are symmetrical with respect to one another, the surroundings of each antenna as an element are highly unsymmetrical, since each antenna has three neighbors within one quadrant and none in the other quadrants.

Fig. 2 shows'dummy antennas, A, B, C and D, one positioned at each end of the Adcock rows NS and EW. -The antennas A, B, C and D are each connected to ground through a dummy load L (Fig. 2a) simulating the effective load L on each of the active antennas N, S, E and W. The antenna A is placed so as to balance the effectof the antenna S on the antenna N; the antenna B balances the eifect of the antenna W on the antenna E, and so on. The degree of symmetry at each antenna obtained by this arrangement is of limited practical advantage, because there is nothing to balance the efiects of the antennas N and S on the antenna E, for example,

and the antennas A and C contribute a still further unbalancing effect at the antenna E.

In order to surround each antenna symmetrically as to nearest neighbors, the system of Fig.

3 is necessary, employing eight dummy or balancing auxiliary antenna A, A", B, B", C, C" and D, D. The antenna E has, in addition to its nearest neighbors B, B", N and S, the nextnearest neighbors A, W, and C. Antenna A" and C are symmetrical with respect to E, but antenna W is not.

Fig. 4 shows an array providing symmetry both of nearest and next nearest neighbors; this is a combination of Figs. 2 and 3 and shields the active antennas from the edge of the ground mat G as well as providing symmetry. While this method may be extended to provide symmetry of each active antenna with respect to third nearest neighbors (such as N and B), such refinement is not usually necessary.

dummy antennas required to compensate the first two sets of neighbors. The antennas A, B, C and D of Fig. 4 are simply moved radially toward thecenterto2p0ints A"",ZB", C', and D', which'are the same distance from the antennas N, E, S and W as i the antenna R.

In the arrangement of Fig. 5 there are some relatively close third order neighbors (such as N' and B); these can be shielded out by the arrangement of Fig. 6, in which the antennas AB, 'BC, CD and DA are added, providingasquarecom prising four nearest neighbors and four second nearest neighbors around eachactive antenna.

Thus the invention ha been described as a method of and means for preventing anomalous response of an Adcock antenna system caused by dissymmetries'inthesurroundings of the individual-antenn'as. A plurality of "auxiliary antennasare setup in positions around the Adcock antennassuch asto'provide approximate positional symmetry-around each' active antenna. The auxiliary antennas are grounded through dummy loads substantially equivalent to the active load of each-'active'an'tenna "to provide electrical symmetry.

I claim as -my invention:

'1. In ara'diodirection"finder system, an 'Adco'ck-antenna'arra-y including spaced-vertical antennas connected to direction indicating apparatus, and a'plurality of auxiliary antennas' so'positioned with respect to the'antennas of said Adcockarray that the nearest-and the second'nearestnei'ghboring'antennas of each of said Adcock antennas are radially symmetrical with respect to -said Adcock antennas.

2. The system *as claimed in claim '1, wherein each of said auxiliary antennas is connected to an electricalloadsubstantiallyequivalent to the load on 'each of the antennas of said Adccok array.

3. An antenna system'including four collector elements positioned at the corners of a square and connected to direction indicating means, 'auxiliaryantenna'elements positioned outside said square and in alignment with the sides thereof, each of said auxiliary elements being at a'distance from thenearest of said collector elements which is equal-to the distance from said nearest collector element to the other collector element lying in the same line, further auxiliary antenna elements positioned outside said square and in alignment with the diagonals thereof, each of said further elements being at a distance from the nearest of said collector elements which is equal to the distance from said nearest collector element to the other collector element lying in the same line, whereby the elements surrounding each of said collector elements are radially symmetrical with respect thereto as to nearest and "next-nearest neighbors, and electrical loads, substantially equivalent to the load presented by said direction indicatormeans to each of said collector lementsconnectedzto said auxiliary antenna elements.

4. An antenna system for radio direction finders including :a group of spaced collector elements connected to utilization circuits and a plurality-of auxiliary antenna elements connected to loads substantially equivalent to that presented by said utilization circuits to each of said collector elements, said auxiliary-elements'being so positioned withrespect to each other and said collector elements as to provide substantial radial symmetry of "the-elements surrounding each of said collector elements.

*5. -An antenna systemincludingcollector elementspositioned respectively at the corners-and at the center-of a square, auxiliary antenna elements positioned outside said square; and in alignment withthe sides and the diagonals thereof, each-of -said auxiliary elements being at a "distance from the nearest of said collector elements which is "equal'tothedistance from said'nearest collector element to the next nearest collector element lying Y in the same line.

"6.The invention as set forth in claim 5, including further auxiliary-elements lying in lines extending through the center of said square and parallel to the-sides thereof, said further elements being equidistant from said center.

DAVID G. C. LUCK.

REFERENCES CITED The .following references are .of .record in the file of'this patent:

UNITED STATES i'PATENTS Number Name Date 2,153,975 Smith et al Apr. 11, 1939 1',738';522 Campbell 'Dec.. 10, 1929 2,126,531 Carter Aug. 9, 1938 

